This invention relates to face seal rings having waves, tilts and a dam. The invention also relates to a seal which utilizes wavy-tilt-dam shaped rings. The invention further relates to an apparatus for making face seal rings.
In conventional face seals where no deliberate means of controlling the shape of the fluid film is used, operating life can be shorter than desired, particularly in high speed, high pressure applications or where operating conditions change frequently or are of great magnitude. A longer life seal having greater reliability would be of considerable economic benefit in many applications.
Seals often fail ultimately by allowing excessive leakage. This type of failure is caused by the faces wearing out, thermal cracking of a face, or poorly distributed wear. The key to minimizing this type of problem is to minimize actual mechanical contact of the faces while, at the same time, maintaining a small gap between the faces. To do this requires that most of the load on the face be supported by fluid pressure (which causes much lower friction than mechanical contact and virtually no wear). Such fluid pressure load support is commonly called thick film lubrication.
It is very difficult in the prior art to control the sealing fluid to provide just enough pressure so as to support most of the load, yet not too much pressure so as to cause the faces to separate and leak excessively. One must control the shape of the seal gap very precisely so that hydrostatic and hydrodynamic pressures develop, and yet minimize the leakage gap. Several prior art patents, which are discussed below, disclose this objective.
U.S. Pat. No. 4,407,512, entitled HIGH PRESSURE ROTARY MECHANICAL SEAL, to Trytek, discloses the use of hydropads to enhance lubrication. Hydropads are semicircular shallow recesses cut into one of the faces and positioned so that they are open to pressure at the edge of the seal ring and terminate part way across. These pads ensure that more lubricant is present. However, the disadvantages of hydropads are: (1) They do not provide hydrostatic lift; and, (2) They do not provide hydrodynamic lift unless the recesses are very shallow, in which case machining is difficult and the shallow recesses tend to wear away.
U.S. Pat. No. 4,290,613, entitled POSITIVE CLEARANCE RADIAL FACE SEALS to Scott, discloses a deflectable face to control clearance. The deflectable face deforms to a shape which forms a converging film. Although the Scott invention is a creative concept, it suffers from the disadvantages of complexity, high cost of manufacture, inability to compensate for wear, lack of hydrodynamic load support, and high leakage associated with a radially convergent seal having no sealing dam.
Other patents disclose various patterns of seal ring grooves to enhance lubrication. U.S. Pat. No. 3,744,805, entitled SLIDE RINGS FOR AXIALLY ACTING SHAFT SEALING RINGS, to Heinrich, discloses many types of groove patterns extending partially across the face of a seal ring. U.S. Pat. No. 4,420,162, entitled MECHANICAL SEAL AND METHOD OF FORMING A SLIDlNG SURFACE THEREOF, to Yamai et al., discloses grooves which extend all across the face of the seal ring in various patterns. The supply of lubricant is improved with both of these seals, but the grooves themselves do not increase hydrodynamic lubrication.
U.S. Pat. No. 3,738,667, entitled SELF-ENERGIZING FACE SEALS, to Symons, discloses a design feature which causes natural waves to develop and enhance lubrication. U.S. Pat. No. 4,212,475, entitled SELF ALIGNING SPIRAL GROOVE FACE SEAL, to Sedy, discloses the use of spiral grooves to improve hydrodynamic lubrication. Both of the patterns on these seal rings are widely different from the seal ring shape of the present invention.
A moving wave mechanical face seal has been described in A.O. Lebeck, Design of an Optimum Moving Wave and Tilt Mechanical Face Seal for Liquid Applications, "9th International Conference on Fluid Sealing, Apr. 1-3, 1981; A.O. Lebeck and L.A. Young, "The Wavy Mechanical Face Seal, Theoretical and Experimental Results," Summary Report ME-111(81)ONR-414-1, Bureau of Engineering Research, January 1981; A.O. Lebeck et al., "Application of the Wavy Mechanical Face Seal to Submarine Seal Design," Report No. ME-117(82)ONR-414-1, Bureau of Engineering Research, July 1982; and L.A. Young and A.O. Lebeck, "The Design and Testing of Moving Wave Mechanical Face Seals Under Variable Operating Conditions in Water," Preprint No. 85-7C-1C-1, American Society of Lubrication Engineers, October 1985. The seal ring in this face seal is made of a flexible material which is deformed during operation into a wavy shape. To prevent uneven wear of the soft flexible material, the seal provides for slowly "moving" the wave on the face of the ring independently of the rotation of the ring. Although this moving wave seal invention achieves enhanced performance characteristics due to the wave shape, it has several disadvantages: (1) The ring cannot be utilized in standard seal systems and requires a great number of additional complex parts; and (2) The cost of manufacture is too high.
Accordingly, it is an object of the present invention to provide a unique wavy-tilt-dam seal ring which promotes hydrostatic and hydrodynamic lubrication and yet minimizes leakage of a seal.
It is another object of the present invention to provide a wavy-tilt-dam seal ring with an extremely long life, even under arduous operating conditions.
Yet another object of the present invention is to provide a seal having enhanced lubrication characteristics, a minimal number of parts, and which can be manufactured and operated at a low cost.
Another object of the present invention is to provide a seal with predictable and consistent operating parameters.
Still another object of the present invention is to provide a grinding apparatus which produces high precision contours on face seal rings at a low cost.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description to follow, taken in conjunction with the accompanying drawing.